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Normals calculation breaking
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Short description of error
Normals go inverted for no obvious reason and recalculation of the normals can fail to "fix" them

Exact steps for others to reproduce the error

  • Load the attached blend

  • Go to Edit Mode
  • Go Top View
  • Select all if not already selected
  • Press CTRL+N to fix the normals and observe how some inverted ones are fixed (by why not all considering those are repeated motif , their geometry/orientation is the same ?)
  • Press CTRL+N again and it's back to before

Making it so you need to fix those manually if you ever hope to add a solidify modifier by example (as the solidify follow the normals, you would end with very bad results if not all the normals are correct)
Fixing that manually is of course a solution on this kind of model because it's still small, but on more complex one, you can see how impractical this is



Event Timeline

Sanc Tuary (sanctuary) raised the priority of this task from to Needs Triage by Developer.
Sanc Tuary (sanctuary) updated the task description. (Show Details)
Sanc Tuary (sanctuary) set Type to Bug.
Bastien Montagne (mont29) claimed this task.

Thanks for the report, but this is not considered a bug.

Thing is, your rings are 100% flat, so there is no real 'inside' nor 'outside', so 'Recalculate Inside/Ouside' operator (called with ctrl-N) more or less gives random result in this case (probably driven by float precision limits). You just have to use Invert Normal operator on rings that are not OK after ctrl-N…